The Rockwell B-1B Lancer is an improved variant of the B-1A, which was initially developed in the 1970s as a replacement for the B-52. Four prototypes of this long-range, high-speed strategic bomber were developed and tested, but the program was canceled in 1977 before production. The B-1B program began in 1981, the first production aircraft flew in October 1984, and the first B-1B was delivered to Dyess AFB, Texas, in June 1985. The aircraft holds almost 50 world records for speed, payload, range, and time of climb in its class. It was first used in combat in support of operations against Iraq during Operation Desert Fox in December 1988. In 1999, six B-1s were used in Operation Allied Force, delivering more than 20 percent of the total ordnance while flying less than 2 percent of the combat sorties. Eight B-1s were deployed in support of Operation Enduring Freedom, and B-1s dropped nearly 40 percent of the total tonnage during the first six months of OEF. Its specifications include a length of 146 feet, a height of 34 feet, a wingspan of 137 feet, a maximum weight of 477,000 pounds, four GE F-101-GE-102 turbofan engines with afterburner, intercontinental unrefueled range, maximum speed of 900-plus miles per hour, a ceiling of 30,000 feet, a crew of four, and armament of 24 GBU-31GPS-aided JDAM or 24 MK-84 general purpose bombs.